Surface Modification to Control Protein/Surface Interactions

Impregnation of polyethylene terephthalate (PET) grafts with BMP-2 loaded functional nanoparticles for reconstruction of anterior cruciate ligament

Current artificial ligaments based on polyethylene terephthalate (PET) are associated with some disadvantages due to their hydrophobicity and low biocompatibility. In this study, we aimed to modify the surface of PET using polyethylene glycol (PEG)-terminated polystyrene (PS)-linoleic nanoparticles (PLinaS-g-PEG-NPs). We accomplished that BMP-2 in two different concentrations encapsulated in nanoparticles with an efficiency of 99.71 ± 1.5 and 99.95 ± 2.8%. While the dynamic contact angle of plain PET surface reduced from 116° to 115° after a measurement periods of 10 s, that of PLinaS-g-PEG-NPs modified PET from 80° to 17.5° within 0.35 s. According to in vitro BMP2 release study, BMP-2 was released 13.12 ± 1.76% and 45.47 ± 1.78% from 0.05 and 0.1BMP2-PLinaS-g-PEG-NPs modified PET at the end of 20 days, respectively. Findings from this study revealed that BMP2-PLinaS-g-PEG-NPs has a great potential to improve the artificial PET ligaments, and could be effectively applied for ACL reconstruction.

A Comparative Study of Three Approaches to Fibre's Surface Functionalization

Polyester-based scaffolds are of research interest for the regeneration of a wide spectrum of tissues. However, there is a need to improve scaffold wettability and introduce bioactivity. Surface modification is a widely studied approach for improving scaffold performance and maintaining appropriate bulk properties. In this study, three methods to functionalize the surface of the poly(lactide-co-ε-caprolactone) PLCL fibres using gelatin immobilisation were compared. Hydrolysis, oxygen plasma treatment, and aminolysis were chosen as activation methods to introduce carboxyl (-COOH) and amino (-NH₂) functional groups on the surface before gelatin immobilisation. To covalently attach the gelatin, carbodiimide coupling was chosen for hydrolysed and plasma-treated materials, and glutaraldehyde crosslinking was used in the case of the aminolysed samples. Materials after physical entrapment of gelatin and immobilisation using carbodiimide coupling without previous activation were prepared as controls. The difference in gelatin amount on the surface, impact on the fibres morphology, molecular weight, and mechanical properties were observed depending on the type of modification and applied parameters of activation. It was shown that hydrolysis influences the surface of the material the most, whereas plasma treatment and aminolysis have an effect on the whole volume of the material. Despite this difference, bulk mechanical properties were affected for all the approaches. All materials were completely hydrophilic after functionalization. Cytotoxicity was not recognized for any of the samples. Gelatin immobilisation resulted in improved L929 cell morphology with the best effect for samples activated with hydrolysis and plasma treatment. Our study indicates that the use of any surface activation method should be limited to the lowest concentration/reaction time that enables subsequent satisfactory functionalization and the decision should be based on a specific function that the final scaffold material has to perform.

Temperature-Responsive Polymer Brush Coatings for Advanced Biomedical Applications

Modern biomedical technologies predict the application of materials and devices that not only can comply effectively with specific requirements, but also enable remote control of their functions. One of the most prospective materials for these advanced biomedical applications are materials based on temperature-responsive polymer brush coatings (TRPBCs). In this review, methods for the fabrication and characterization of TRPBCs are summarized, and possibilities for their application, as well as the advantages and disadvantages of the TRPBCs, are presented in detail. Special attention is paid to the mechanisms of thermo-responsibility of the TRPBCs. Applications of TRPBCs for temperature-switchable bacteria killing, temperature-controlled protein adsorption, cell culture, and temperature-controlled adhesion/detachment of cells and tissues are considered. The specific criteria required for the desired biomedical applications of TRPBCs are presented and discussed.

Immunospecific analysis of in vitro and ex vivo surface-immobilized protein complex

Biomaterials used for blood contacting devices are inherently thrombogenic. Antithrombotic agents can be used as surface modifiers on biomaterials to reduce thrombus formation on the surface and to maintain device efficacy. For quality control and to assess the effectiveness of immobilization strategies, it is necessary to quantify the surface-immobilized antithrombotic agent directly. There are limited methods that allow direct quantification on device surfaces such as catheters. In this study, an enzyme immunoassay (EIA) has been developed to measure the density of a synthetic antithrombin-heparin (ATH) covalent complex immobilized on a catheter surface. The distribution of the immobilized ATH was further characterized by an immunohistochemical assay. This analyte-specific EIA is relatively simple and has high throughput, thus providing a tool for quantitative analysis of biomaterial surface modifications. These methods may be further modified to evaluate plasma proteins adsorbed and immobilized on various biomaterial surfaces of complex shapes, with a range of bioactive functionalities, as well as to assess conformational changes of proteins using specific antibodies.

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Novel Antimicrobial Surfaces to Defeat COVID-19 Transmission

Antimicrobial surface coatings function as a contact biocide and are extensively used to prevent the growth and transmission of pathogens on environmental surfaces. Currently, scientists and researchers are intensively working to develop antimicrobial, antiviral coating solutions that would efficiently impede/stop the contagion of COVID-19 via surface contamination. Herein we present a flavonoid-based antimicrobial surface coating fabricated by laser processing that has the potential to eradicate COVID-19 contact transmission. Quercetin-containing coatings showed better resistance to microbial colonization than antibiotic–containing ones.

Corrosion Behavior and In Vitro Cytotoxicity of Ni-Ti and Stainless Steel Arch Wires Exposed to Lysozyme, Ovalbumin, and Bovine Serum Albumin

In this study, the tendency and mechanisms by which protein and mechanical loads contribute to corrosion were determined by exposing Ni-Ti and stainless steel arch wires under varying mechanical loads to artificial saliva containing different types of protein (lysozyme, ovalbumin, and bovine serum albumin). The corrosion behavior and in vitro cytotoxicity results show that exposure to both protein and mechanical stress significantly decreased the corrosion resistance of stainless steel and increased the release of toxic corrosion products. Adding protein inhibited the corrosion of Ni-Ti, but the mechanical loads counteracted this effect. Even proteins containing the same types of amino acids had different effects on the corrosion resistance of the same alloy. The effect of protein or stress, or their combination, should be considered in the application of metal medical materials.

Supramolecular Additive-Initiated Controlled Atom Transfer Radical Polymerization of Zwitterionic Polymers on Ureido-pyrimidinone-Based Biomaterial Surfaces

Surface-initiated controlled radical polymerization is a popular technique for the modification of biomaterials with, for example, antifouling polymers. Here, we report on the functionalization of a supramolecular biomaterial with zwitterionic poly(sulfobetaine methacrylate) via atom transfer radical polymerization from a macroinitiator additive, which is embedded in the hard phase of the ureido-pyrimidinone-based material. Poly(sulfobetaine methacrylate) was successfully polymerized from these surfaces, and the polymerized sulfobetaine content, with corresponding antifouling properties, depended on both the macroinitiator additive concentration and polymerization time. Furthermore, the polymerization from the macroinitiator additive was successfully translated to functional electrospun scaffolds, showing the potential for this functionalization strategy in supramolecular material systems.

Microwave-/UV-assisted Enhancement of the Wettability of Photoactive TiO2 Substrates Coated on an Inactive Ti/i-TiO2 Base

Titanium dioxide (TiO₂) has been proven to be an excellent system for wettability patterning purposes because of its super hydrophilic ability and its oxidative/reductive degradation of substances when exposed to UV radiation. TiO₂ substrates upon which was deposited a self-assembled monolayer (SAM) of n-octadecyltrimethoxysilane (ODS) shifts the surface to become super hydrophobic, which when subjected to UV irradiation causes the ODS compound to be degraded with the substrate turning back to be super hydrophilic. Such events allow wettability patterns to be easily created. The objective of this study was to reduce the time required to construct a wettability pattern. For this purpose, highly photoactive TiO₂ nanoparticles were coated onto a titanium plate whose surface had been previously oxidized at high temperatures in an electric furnace. The subsequent TiO₂/Ti system was microwaved and simultaneously irradiated with ultraviolet light (UV) to further accelerate its photocatalytic activity. Using a set of photomasks and both UV and microwave irradiation, the generation of a pattern was achieved 15 times faster (2 min versus 30 min) compared to an earlier result that used only UV radiation.

Preparation of thermo-responsive PNIPAAm-MWCNT membranes and evaluation of its antifouling properties in dairy wastewater

A novel MWCNT-PNIPAAm nanocomposite membrane was developed with an excellent cleaning efficiency of thermo-responsive surface. The thermo-responsive N-isopropyle acryleamide (NIPAAm) monomer was polymerized on the surface of MWCNT via free radical polymerization. The prepared MWCNT-PNIPAAm nanocomposite was characterized by FTIR, SEM and TGA analyses. Various amounts of the prepared nanocomposite were incorporated into the membrane matrix by the physical blending method. The resultant membranes showed better surface wettability and pure water flux compared to pristine Polyethersulfone (PES) membrane. Furthermore, after filtration, the COD value of dairy wastewater was reduced to around 90% for all membranes. The thermo-responsive cleaning method was employed to investigate the cleaning efficiency of MWCNT-PNIPAAm membrane for dairy wastewater. The 99.9% flux recovery ratio was obtained for MWCNT-PNIPAAm-0.05% membranes. All these results confirmed that the presence of MWCNT-PNIPAAm nanocomposite in the membrane matrix improves the membrane hydrophilicity and antifouling properties.

Electrostatic Adsorption Behavior of Zwitterionic Copolymers on Negatively Charged Surfaces

To investigate the effect of the surface properties and the coating layer properties on surface modification via electrostatic adsorption, the electrostatic adsorption behavior of zwitterionic copolymers on negatively charged surfaces was studied. A series of positively charged zwitterionic copolymers and a series of negatively charged surfaces, including porous substrates and dense films, were fabricated. The electrostatic adsorption behavior of the zwitterionic copolymers on the negatively charged porous substrates was confirmed using the contact angles and fluorescently labeled protein adsorption experiments. The adsorption behavior of the zwitterionic copolymers on the negatively charged dense films was confirmed using quartz crystal microbalance determination and a fluorescently labeled protein adsorption experiment. The results indicated that a lower charge density on the zwitterionic copolymer brings about a higher adsorption mass on the charged surface, whereas an extremely low charge density on the coating layer results in a lower adsorption mass on the charged surface, due to weak interaction. A high density of the film surface charge is beneficial for surface adsorption, whereas an extremely high density of the film surface charge leads to low surface adsorption due to steric hindrance of the negatively charged sites. This work provides an insight into the best strategy for surface modification via electrostatic adsorption.

Self-assembled monolayers of phosphonates promote primary chondrocyte adhesion to silicon dioxide and polyvinyl alcohol materials

The optimal solution for articular cartilage repair has not yet been identified, in part because of the challenges in achieving integration with the host. Coatings have the potential to transform the adhesive features of surfaces, but their application to cartilage repair has been limited. Self-assembled monolayer of phosphonates (SAMPs) have been demonstrated to increase the adhesion of various immortalized cell types to metal and polymer surfaces, but their effect on primary chondrocyte adhesion has not been studied. The objective of this study was to investigate the response of primary chondrocytes to SAMP coatings. We hypothesized a SAMP terminated with an α,ω-bisphosphonic acid, in particular butane-1,4-diphosphonic acid, would increase the number of adherent primary chondrocytes to polyvinyl alcohol (PVA). To test our hypothesis, we first established our ability to successfully modify silicon dioxide (SiO2) surfaces to enable chondrocytes to attach to the surface, without substantial changes in gene expression. Secondly, we applied identical chemistry to PVA, and quantified chondrocyte adhesion. SAMP modification to SiO2 increased chondrocyte adhesion by ×3 after 4 hr and ×4.5 after 24 hr. PVA modification with SAMPs increased chondrocyte adhesion by at least ×31 after 4 and 24 hours. Changes in cell morphology indicated that SAMP modification led to improved chondrocyte adhesion and spreading, without changes in gene expression. In summary, we modified SiO2 and PVA with SAMPs and observed an increase in the number of adherent primary bovine chondrocytes at 4 and 24 hr post-seeding. Mechanisms of chondrocyte interaction with SAMP-modified surfaces require further investigation.

Gold nanoparticle–protein conjugate dually-responsive to pH and temperature for modulation of enzyme activity

The enzymatic activity of the dual-responsive gold nanoparticle–protein–polymer conjugate can be modulated almost in a full range under different pH and temperature conditions.

Regulating the migration of smooth muscle cells by a vertically distributed poly(2-hydroxyethyl methacrylate) gradient on polymer brushes covalently immobilized with RGD peptides

The gradient localization of biological cues is of paramount importance to guide directional migration of cells. In this study, poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate)-block- poly(2-hydroxyethyl methacrylate) (P(HEMA-co-GMA)-b-PHEMA) brushes with a uniform underneath P(HEMA-co-GMA) layer and a gradient thickness of PHEMA blocks were prepared by using surface-initiated atom-transfer radical polymerization and a dynamically controlled polymerization process. The polymer chains were subsequently functionalized with the cell-adhesive arginine-glycine-aspartic acid (RGD) peptides by reaction with the glycidyl groups, and their structures and properties were characterized by X-ray photoelectron spectrometry (XPS), quartz crystal microbalance with dissipation (QCM-D) and air contact angle. Adhesion and migration processes of smooth muscle cells (SMCs) were then studied. Compared with those on the sufficiently exposed RGD surface, the cell adhesion and mobility were well maintained when the RGD peptides were localized at 18.9 nm depth, whereas the adhesion, spreading and migration rate of SMCs were significantly impaired when the RGD peptides were localized at a depth of 38.4 nm. On the RGD depth gradient surface, the SMCs exhibited preferential orientation and enhanced directional migration toward the direction of reduced thickness of the second PHEMA brushes. Half of the cells were oriented within ± 30° to the x-axis direction, and 72% of the cells moved directionally at the optimal conditions. Cell adhesion strength, arrangement of cytoskeleton, and gene and protein expression levels of adhesion-related proteins were studied to corroborate the mechanisms, demonstrating that the cell mobility is regulated by the complex and synergetic intracellular signals resulted from the difference in surface properties.

STATEMENT OF SIGNIFICANCE

Cell migration is of paramount importance for the processes of tissue repair and regeneration. So far, the gradient localization of biological cues perpendicular to the substrate, which is the usual case for the biological signaling molecules to locate in ECM in vivo, has been scarcely studied, and has not been used to guide the directional migration of cells. In this study, we prepare a depth gradient of RGD peptides along the polymer chains, which is used to guide the directional migration of SMCs after a second hydrophilic bock is prepared in a gradient manner. For the first time the directional migration of SMCs is achieved under the guidance of a depth gradient of RGD ligands. The mechanisms of different cell migration abilities are further discussed based on the results of cell adhesion, cell adhesion force, cytoskeleton alignment and expression of relative proteins and genes. This work paves a new strategy by fabricating a gradient polymer brushes with immobilized bioactive molecules to dominate the directional cell migration, and elucidates the mechanisms underlining the biased migration along RGD depth localization gradients, shedding a light for the design of novel biomaterials to control and guide cell migration and invasion.

Nanoplasmonic sensors for biointerfacial science

In recent years, nanoplasmonic sensors have become widely used for the label-free detection of biomolecules across medical, biotechnology, and environmental science applications. To date, many nanoplasmonic sensing strategies have been developed with outstanding measurement capabilities, enabling detection down to the single-molecule level. One of the most promising directions has been surface-based nanoplasmonic sensors, and the potential of such technologies is still emerging. Going beyond detection, surface-based nanoplasmonic sensors open the door to enhanced, quantitative measurement capabilities across the biointerfacial sciences by taking advantage of high surface sensitivity that pairs well with the size of medically important biomacromolecules and biological particulates such as viruses and exosomes. The goal of this review is to introduce the latest advances in nanoplasmonic sensors for the biointerfacial sciences, including ongoing development of nanoparticle and nanohole arrays for exploring different classes of biomacromolecules interacting at solid-liquid interfaces. The measurement principles for nanoplasmonic sensors based on utilizing the localized surface plasmon resonance (LSPR) and extraordinary optical transmission (EOT) phenomena are first introduced. The following sections are then categorized around different themes within the biointerfacial sciences, specifically protein binding and conformational changes, lipid membrane fabrication, membrane-protein interactions, exosome and virus detection and analysis, and probing nucleic acid conformations and binding interactions. Across these themes, we discuss the growing trend to utilize nanoplasmonic sensors for advanced measurement capabilities, including positional sensing, biomacromolecular conformation analysis, and real-time kinetic monitoring of complex biological interactions. Altogether, these advances highlight the rich potential of nanoplasmonic sensors and the future growth prospects of the community as a whole. With ongoing development of commercial nanoplasmonic sensors and analytical models to interpret corresponding measurement data in the context of biologically relevant interactions, there is significant opportunity to utilize nanoplasmonic sensing strategies for not only fundamental biointerfacial science, but also translational science applications related to clinical medicine and pharmaceutical drug development among countless possibilities.

Design of Antibacterial Poly(ether sulfone) Membranes via Covalently Attaching Hydrogel Thin Layers Loaded with Ag Nanoparticles

To inhibit bacteria attachment and the subsequent formation of biofilms on poly(ether sulfone) (PES) membranes, poly(sulfobetaine methacrylate)/poly(sodium acrylate) antibacterial hydrogel thin layers were covalently attached onto the membranes, followed by loading with Ag nanoparticles. In our strategy, double bonds were firstly introduced onto the PES membrane surfaces to provide anchoring sites, and then the hydrogel layers were synthesized on the membrane surfaces via UV light-initiated crosslinking copolymerization. Then, Ag ions were adsorbed into the hydrogel layers and reduced to Ag nanoparticles by sodium borohydride. The amounts of the adsorbed Ag ions were controlled by the mole ratios of carboxylate groups in the hydrogel layers. After attaching the hydrogel layers, a typical 3D porous structure was observed by scanning electron microscopy, and the surface chemical composition variations were characterized by attenuated total reflection-Fourier transform infrared spectroscopy. The live/dead staining, inhibition zone, and the optical degree of co-culture solution demonstrated that the designed surfaces could not only effectively resist bacteria attachment but also kill the surrounding bacteria Escherichia coli and Staphylococcus aureus. It was noteworthy that the strong antibacterial ability could be maintained for more than 5 weeks. Additionally, the excellent hemocompatibility of the modified membranes was confirmed by undetectable plasma protein adsorption, suppressed platelet adhesion, prolonged clotting time, low hemolysis ratio, and suppressed blood-related complement activation. Cell culture tests indicated that the membranes showed no cytotoxicity, but strong anti-cell adhesion properties. The proposed method to fabricate antibacterial hydrogel thin layers has great potential to be widely used to inhibit the formation of biofilms on various biomedical devices.

Measuring the Surface-Surface Interactions Induced by Serum Proteins in a Physiological Environment

In this work, we applied total internal reflection microscopy (TIRM) to directly measure the interactions between three different kinds of macroscopic surfaces: namely bare polystyrene (PS) particle and bare silica surface (bare-PS/bare-silica), PS particle and silica surfaces both coated with bovine serum albumin (BSA) (BSA-PS/BSA-silica), and PS particle and silica surfaces both modified with polyethylene glycol (PEG) (PEG-PS/PEG-silica) polymers, in phosphate buffer solution (PBS) and fetal bovine serum (FBS). Our results showed that in PBS, all the bare-PS, BSA-PS, and PEG-PS particles were irreversibly deposited onto the bare silica surface or surfaces coated either with BSA or PEG. However, in FBS, the interaction potentials between the particle and surface exhibited both free-diffusing particle and stuck particle profiles. Dynamic light scattering (DLS) and elliposmeter measurements indicated that there was a layer of serum proteins adsorbed on the PS particle and silica surface. TIRM measurement revealed that such adsorbed serum proteins can mediate the surface-surface interactions by providing additional stabilization under certain conditions, but also promoting bridging effect between the two surfaces. The measured potential profile of the stuck particle in FBS thus was much wider than in PBS. These quantitative measurements provide insights that serum proteins adsorbed onto surfaces can regulate surface-surface interactions, thus leading to unique moving behavior and stability of colloidal particles in the serum environment.

Protein-surface interactions on stimuli-responsive polymeric biomaterials

Responsive surfaces: a review of the dependence of protein adsorption on the reversible volume phase transition in stimuli-responsive polymers. Specifically addressed are a widely studied subset: thermoresponsive polymers. Findings are also generalizable to other materials which undergo a similarly reversible volume phase transition. As of 2015, over 100,000 articles have been published on stimuli-responsive polymers and many more on protein-biomaterial interactions. Significantly, fewer than 100 of these have focused specifically on protein interactions with stimuli-responsive polymers. These report a clear trend of increased protein adsorption in the collapsed state compared to the swollen state. This control over protein interactions makes stimuli-responsive polymers highly useful in biomedical applications such as wound repair scaffolds, on-demand drug delivery, and antifouling surfaces. Outstanding questions are whether the protein adsorption is reversible with the volume phase transition and whether there is a time-dependence. A clear understanding of protein interactions with stimuli-responsive polymers will advance theoretical models, experimental results, and biomedical applications.

Combined Chemical Groups and Topographical Nanopattern on the Poly(ε-Caprolactone) Surface for Regulating Human Foreskin Fibroblasts Behavior

Surface chemistry and substrate topography could contribute significantly to providing a biochemical and topographical cues for governing the fate of cells on the cell-material interface. However, the synergies between these two properties have not been exploited extensively for biomaterial design. Herein, we achieved spatial-controlled patterning of chemical groups on the poly(ε-caprolactone) (PCL) surface by elegant UV-nanoimprint lithography (UN-NIL). The introduction of chemical groups on the PCL surface was developed by our newly 6-benzyloxycarbonylmethyl-ε-caprolactone (BCL) monomer, which not only solved the lack of functional groups along the PCL chain but also retained the original favorable properties of PCL materials. The synergetic effect of the chemical groups and nanopatterns on the human foreskin fibroblasts (HFFs) behaviors was evaluated in detail. The results revealed that the patterned functional PCL surfaces could induce enhanced cell adhesion and proliferation, further trigger changes in HFFs morphology, orientation and collagen secretion. Taken together, this study provided a method for straightforward fabrication of reactive PCL surfaces with topographic patterns by one-step process, and they would facilitate PCL as potential candidate for cell cultivation and tissue engineering.

Dual-function antibacterial surfaces for biomedical applications

Bacterial attachment and the subsequent formation of biofilm on surfaces of synthetic materials pose a serious problem in both human healthcare and industrial applications. In recent decades, considerable attention has been paid to developing antibacterial surfaces to reduce the extent of initial bacterial attachment and thereby to prevent subsequent biofilm formation. Briefly, there are three main types of antibacterial surfaces: bactericidal surfaces, bacteria-resistant surfaces, and bacteria-release surfaces. The strategy adopted to develop each type of surface has inherent advantages and disadvantages; many efforts have been focused on the development of novel antibacterial surfaces with dual functionality. In this review, we highlight the recent progress made in the development of dual-function antibacterial surfaces for biomedical applications. These surfaces are based on the combination of two strategies into one system, which can kill attached bacteria as well as resisting or releasing bacteria. Perspectives on future research directions for the design of dual-function antibacterial surfaces are also provided.

Measurements of long-range interactions between protein-functionalized surfaces by total internal reflection microscopy

Understanding the interaction between protein-functionalized surfaces is an important subject in a variety of protein-related processes, ranging from coatings for biomedical implants to targeted drug carriers and biosensors. In this work, utilizing a total internal reflection microscope (TIRM), we have directly measured the interactions between micron-sized particles decorated with three types of common proteins concanavalin A (ConA), bovine serum albumin (BSA), lysozyme (LYZ), and glass surface coated with soy proteins (SP). Our results show that the protein adsorption greatly affects the charge property of the surfaces, and the interactions between those protein-functionalized surfaces depend on solution pH values. At pH 7.5-10.0, all these three protein-functionalized particles are highly negatively charged, and they move freely above the negatively charged SP-functionalized surface. The net interaction between protein-functionalized surfaces captured by TIRM was found as a long-range, nonspecific double-layer repulsion. When pH was decreased to 5.0, both protein-functionalized surfaces became neutral and double-layer repulsion was greatly reduced, resulting in adhesion of all three protein-functionalized particles to the SP-functionalized surface due to the hydrophobic attraction. The situation is very different at pH = 4.0: BSA-decorated particles, which are highly charged, can move freely above the SP-functionalized surfaces, while ConA- and LYZ-decorated particles can only move restrictively in a limited range. Our results quantify these nonspecific kT-scale interactions between protein-functionalized surfaces, which will enable the design of surfaces for use in biomedical applications and study of biomolecular interactions.

Selectively splitting a droplet using superhydrophobic stripes on hydrophilic surfaces

The droplet can be split by impinging on the hybrid hydrophobic–hydrophilic surface at a high velocity.

Antibiofouling polymer interfaces: poly(ethylene glycol) and other promising candidates

This review highlights antibiofouling polymer interfaces with emphasis on the latest developments using poly(ethylene glycol) and the design new polymeric structures.

Simple surface treatment of cell-culture scaffolds with ultrafine bubble water

We propose a novel method to treat polymeric scaffold surfaces for cell culture with water containing nanobubbles, called ultrafine bubbles (UFBs), with typical diameters less than 1 μm. A thin film of polystyrene (PS) prepared on a solid substrate was exposed to UFB water for 2 days at room temperature. The PS surface was characterized by X-ray photoelectron spectroscopy (XPS), static contact angle measurements in water, and atomic force microscopy (AFM). The surface chemical composition and wettability of PS films remained unchanged after treatment, so that aggregation states of PS at film surfaces remained unaltered by UFB water. On the other hand, after treatment, many UFBs were adsorbed on hydrophobic PS surfaces. To study the effect of UFBs on scaffold properties, the adsorption behavior of fibronectin, which is a typical extracellular matrix protein involved in cell adhesion and proliferation, was examined. While the effect on the adsorption was unclear, the structural denaturation of fibronectin was enhanced after UFB treatment, so that the proliferation of fibroblast cells on PS surfaces was promoted.

Blood compatible materials: state of the art

Devices that function in contact with blood are ubiquitous in clinical medicine and biotechnology. These devices include vascular grafts, coronary stents, heart valves, catheters, hemodialysers, heart-lung bypass systems and many others. Blood contact generally leads to thrombosis (among other adverse outcomes), and no material has yet been developed which remains thrombus-free indefinitely and in all situations: extracorporeally, in the venous circulation and in the arterial circulation. In this article knowledge on blood-material interactions and "thromboresistant" materials is reviewed. Current approaches to the development of thromboresistant materials are discussed including surface passivation; incorporation and/or release of anticoagulants, antiplatelet agents and thrombolytic agents; and mimicry of the vascular endothelium.

Thermoresponsive copolymer decorated surface enables controlling the adsorption of a target protein in plasma

The control of protein/surface interactions by external stimuli is often required in bioapplications such as bioseparation and biosensors. Although regulation of protein adsorption has been achieved on the surfaces modified with stimuli-responsive polymers, controlled protein adsorption is still challenging for a target protein in a multiprotein system. The present study developed a concept of surface design for the controlled adsorption of a specific protein from plasma by combining a thermoresponsive polymer with an affinity ligand on the surface. In this regard, a polyurethane (PU) surface was modified with the copolymer of N-isopropylacrylamide (NIPAAm) and a ε-lysine-containing monomer (LysMA). ε-Lysine is a specific ligand for plasminogen that was used as the model "target protein" in this study. The PU-P(NIPAAm-co-Lys) surfaces exhibited distinct thermoresponsivity of plasminogen adsorption from plasma with a larger quantity adsorbed at 37 °C than at 23 °C. By contrast, the surfaces showed a low level of adsorption for other plasma proteins at both temperatures. In addition, plasminogen adsorbed on a PU-P(NIPAAm-co-Lys) surface could be partly desorbed by lowering the temperature, and the activity of plasminogen adsorbed was well preserved. We believe that the concept developed in this study can be extended to other proteins by combining PNIPAAm and specific ligands with affinities for the proteins of interest.

A density gradient of basic fibroblast growth factor guides directional migration of vascular smooth muscle cells

The migration of vascular smooth muscle cells (VSMCs) is an important process in many physiological events. It is of paramount importance to control the migration rate and direction of VSMCs by biomaterials. In this paper, a density gradient of basic fibroblast growth factor (bFGF) was fabricated using an injection method and the bio-conjugation between heparin and bFGF. The density of bFGF gradually increased with a slope of 17 ng/cm(2)/mm. Adhesion and migration of VSMCs were studied on the bFGF gradient. The VSMCs exhibited preferential orientation and an enhanced directional migration behavior on the gradient surface. Up to 70% cells migrated towards the region with a higher density of bFGF on the gradient. However, the bFGF gradient had no effect on the cell migration rate.

125I-radiolabeling, surface plasmon resonance, and quartz crystal microbalance with dissipation: three tools to compare protein adsorption on surfaces of different wettability

The extent of protein adsorption is an important consideration in the biocompatibility of biomaterials. Various experimental methods can be used to determine the quantity of protein adsorbed, but the results usually differ. In the present work, self-assembled monolayers (SAMs) were used to prepare a series of model gold surfaces varying systematically in water wettability, from hydrophilic to hydrophobic. Three commonly used methods, namely, surface plasmon resonance (SPR), quartz crystal microbalance with dissipation (QCM-D), and (125)I-radiolabeling, were employed to quantify fibrinogen (Fg) adsorption on these surfaces. This approach allows a direct comparison of the mass of Fg adsorbed using these three techniques. The results from all three methods showed that protein adsorption increases with increasing surface hydrophobicity. The increase in the mass of Fg adsorbed with increasing surface hydrophobicity in the SPR data was parallel to that from (125)I-radiolabeling, but the absolute values were different and there does not seem to be a "universally congruent" relationship between the two methods for surfaces with varying wettability. For QCM-D, the variation in protein adsorption with wettability was different from that for SPR and radiolabeling. On the more hydrophobic surfaces, QCM-D gave an adsorbed mass much higher than from the two other methods, possibly because QCM-D measures both the adsorbed Fg and its associated water. However, on the more hydrophilic surfaces, the adsorbed mass from QCM-D was slightly greater than that from SPR, and both were smaller than from (125)I-radiolabeling; this was true no matter whether the Sauerbrey equation or the Voigt model was used to convert QCM-D data to adsorbed mass.

Characterization and bioactive properties of zirconia based polymeric hybrid for orthopedic applications

Zirconia is a transition metal oxide with current applications to orthopedic implants. It has been shown to up-regulate specific genes involved in bio-integration and injury repair. This study examines the effects of zirconia and polydimethylsiloxane (PDMS) hybrids on the proliferation and viability of human primary osteoblast and fibroblast cells. In this study, zirconia-PDMS hybrid coatings were synthesized using a modified sol gel process. The hybrid material was characterized using optical microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle analysis. This study demonstrates that Zr-PMDS surface materials display hydrophobic surface properties coupled with a preferential deposition of polymer near the surface. Primary osteoblast and fibroblast proliferation and viability on hybrid coated surfaces were evaluated via a rapid screening methodology using WST-1 and calcein AM assays. The cells were seed at 5,000 cells per well in 96-well plates coated with various composition of Zr-PDMS hybrids. The results showed increasing cell proliferation with increasing zirconia concentration, which peaked at 90 % v/v zirconia. Proliferation of osteoblasts and fibroblasts displayed similar trends on the hybrid material, although osteoblasts displayed a bi-phasic dose response by the calcein AM assay. The results of this current study show that Zr-PDMS may be used to influence tissue-implant integration, supporting the use of the hybrid as a promising coating for orthopedic trauma implants.

Combining surface topography with polymer chemistry: exploring new interfacial biological phenomena

This review focuses on combining surface topography and surface chemical modification by the grafting of polymers to develop optimal material interfaces with synergistic properties and functions for biological and biomedical applications.

Interaction of preosteoblasts with surface-immobilized collagen-based nanotubes

In a previous work, we demonstrated the successful use of electrophoretic deposition (EPD) to immobilize collagen-based nanotubes onto indium-tin-oxide-coated glass (ITO glass), leading to the creation of biointerfaces with protein-based chemistry and topography [1]. In this work, we present a first study of preosteoblasts behavior in contact with surface-immobilized collagen-based nanotubes. Changes in cell morphology after their interaction with ITO glass modified with collagen-based nanotubes were studied using fluorescence microscopy and compared to those observed on virgin ITO glass as well as on ITO glass on which a collagen layer was simply adsorbed. Scanning electron microscopy (SEM) was used to study interactions of cell filopodias with the deposited nanotubes. Cytotoxicity of these biointerfaces was examined as well in short term cultures, using Alamar blue assay. Cells showed particular morphologies on ITO glass coated with nanotubes compared to virgin ITO glass or collagen adsorbed layer on ITO glass. High resolution SEM images suggest that apart from cell morphology, length and thickness of filopodias seem to be significantly affected by surface modification with collagen-based nanotubes. Moreover, nanotube-coated ITO glass did not show any obvious cytotoxicity in short term culture, opening new perspectives for the surface modification of biomaterials. We show the versatility of the proposed surface modification procedure by tailoring biointerfaces with a mixture of micro- and nanometer-scale collagen-based tubes.

Thermally responsive silicon nanowire arrays for native/denatured-protein separation

We present our findings of the selective adsorption of native and denatured proteins onto thermally responsive, native-protein resistant poly(N-isopropylacrylamide) (PNIPAAm) decorated silicon nanowire arrays (SiNWAs). The PNIPAAm-SiNWAs surface, which shows very low levels of native-protein adsorption, favors the adsorption of denatured proteins. The amount of denatured-protein adsorption is higher at temperatures above the lower critical solution temperature (LCST) of PNIPAAm. Temperature cycling surrounding the LCST, which ensures against thermal denaturation of native proteins, further increases the amount of denatured-protein adsorption. Moreover, the PNIPAAm-SiNWAs surface is able to selectively adsorb denatured protein even from mixtures of different protein species; meanwhile, the amount of native proteins in solution is kept nearly at its original level. It is believed that these results will not only enrich current understanding of protein interactions with PNIPAAm-modified SiNWAs surfaces, but may also stimulate applications of PNIPAAm-SiNWAs surfaces for native/denatured protein separation.

Combinatorial on-chip study of miniaturized 3D porous scaffolds using a patterned superhydrophobic platform

One of the main challenges in tissue engineering (TE) is to obtain optimized products, combining biomaterials, cells and soluble factors able to stimulate tissue regeneration. Multiple combinations may be considered by changing the conditions among these three factors. The unpredictable response of each combination requires time-consuming tests. High-throughput methodologies have been proposed to master such complex analyses in TE. Usually, these tests are performed using cells cultured into 2D biomaterials or by dispensing arrays of cell-loaded hydrogels. For the first time an on-chip combinatorial study of 3D miniaturized porous scaffolds is proposed, using a patterned bioinspired superhydrophobic platform. Arrays of biomaterials are dispensed and processed in situ as porous scaffolds with distinct composition, surface characteristics, porosity/pore size, and mechanical properties. On-chip porosity, pore size, and mechanical properties of scaffolds based on chitosan and alginate are assessed by adapting microcomputed tomography equipment and a dynamic mechanical analyzer, as well as cell response after 24 hours. The interactions between cell types of two distinct origins-osteoblast-like and fibroblasts-and the scaffolds modified with fibronectin are studied and validated by comparison with conventional destructive methods (dsDNA quantification and MTS tests). Physical and biological on-chip analyses are coherent with the conventional measures, and conclusions about the most favorable conditions for each cell type are taken.

Emerging applications of superhydrophilic-superhydrophobic micropatterns

Water on superhydrophilic surfaces spreads or is absorbed very quickly, and exhibits water contact angles close to zero. We encounter superhydrophilic materials in our daily life (e.g., paper, sponges, textiles) and they are also ubiquitous in nature (e.g., plant and tree leaves, Nepenthes pitcher plant). On the other hand, water on completely non-wettable, superhydrophobic surfaces forms spherical droplets and rolls off the surface easily. One of the most well-known examples of a superhydrophobic surface is the lotus leaf. Creating novel superhydrophobic surfaces has led to exciting new properties such as complete water repellency, self-cleaning, separation of oil and water, and antibiofouling. However, combining these two extreme states of superhydrophilicity and superhydrophobicity on the same surface in precise two-dimensional micropatterns opens exciting new functionalities and possibilities in a wide variety of applications from cell, droplet, and hydrogel microarrays for screening to surface tension confined microchannels for separation and diagnostic devices. In this Progress Report, we briefly describe the methods for fabricating superhydrophilic-superhydrophobic patterns and highlight some of the newer and emerging applications of these patterned substrates that are currently being explored. We also give an outlook on current and future applications that would benefit from using such superhydrophilic-superhydrophobic micropatterns.

Orchestrating cell/material interactions for tissue engineering of surgical implants

Research groups are currently recognising a critical clinical need for innovative approaches to organ failure and agenesis. Allografting, autologous reconstruction and prosthetics are hampered with severe limitations. Pertinently, readily available 'laboratory-grown' organs and implants are becoming a reality. Tissue engineering constructs vary in their design complexity depending on the specific structural and functional demands. Expeditious methods on integrating autologous stem cells onto nanoarchitectured 3D nanocomposites, are being transferred from lab to patients with a number of successful first-in-man experiences. Despite the need for a complete understanding of cell/material interactions tissue engineering is offering a plethora of exciting possibilities in regenerative medicine.